Show proper error from init process panic

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

libcontainer/factory_linux.go

@@ -9,6 +9,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"regexp"
+	"runtime/debug"
 	"strconv"
 	"syscall"
 
@@ -248,6 +249,13 @@ func (l *LinuxFactory) StartInitialization() (err error) {
 		// ensure that this pipe is always closed
 		pipe.Close()
 	}()
+
+	defer func() {
+		if e := recover(); e != nil {
+			err = fmt.Errorf("panic from initialization: %v, %v", e, string(debug.Stack()))
+		}
+	}()
+
 	i, err = newContainerInit(it, pipe)
 	if err != nil {
 		return err

libcontainer/process_linux.go

@@ -340,7 +340,7 @@ loop:
 		}
 	}
 	if !sentRun {
-		return newSystemError(fmt.Errorf("could not synchronise with container process"))
+		return newSystemError(fmt.Errorf("could not synchronise with container process: %v", ierr))
 	}
 	if p.config.Config.Namespaces.Contains(configs.NEWNS) && !sentResume {
 		return newSystemError(fmt.Errorf("could not synchronise after executing prestart hooks with container process"))